Please don't rely on the Referer being present (ever). It's an optional header to send in a request and you can configure your browser — at least Firefox — to n

Please don't rely on the Referer being present (ever). It's an optional header to send in a request and you can configure your browser — at least Firefox — to not send it for privacy reasons. Logout (or anything else that triggers changes of any kind) shouldn't be a GET request.